The present invention relates to industrial control systems and the like and in particular to an industrial control system comprised of many distributed controllers dividing job tasks among themselves using “market model” based bids and counter bids.
In a centralized model for industrial control, a single central controller (being a specialized computer) coordinates all aspects of the controlled process. Input signals representing values from sensors on the controlled process are communicated to the central controller which executes a control program to develop output signals which are communicated to actuators on the controlled process.
The centralized model is conceptually simple and requires programming only a single device. Nevertheless, the centralized model has some disadvantages. Control systems using this model are particularly vulnerable to failure of the single central controller. Further, communication of all I/O signals to a central location and executing the control program on a single computer, particularly for large control systems, can place undue burdens on processing resources and communication bandwidth.
In the distributed model for industrial control, the control program is executed by a number of spatially separate controllers intercommunicating only as needed on a common network. By placing these controllers near relevant I/O points, the communication of large amounts of I/O data is diminished. Having multiple control devices can also reduce the susceptibility of the control system to failure of any one device.
One difficulty with distributed control is that of developing the multiple control programs to dividing the control tasks among the various distributed controllers and coordinating their actions. One promising method of both dividing the control task among the controllers and coordinating their actions borrows from a market model of the economy in which many different autonomous individuals organize themselves (through bidding and counter bidding) to produce complex products or services without central control. In such autonomous cooperative systems (ACS), a job description is presented to a large number of autonomous cooperative units (ACUs), which, based on knowledge of their own capabilities and limitations, bid on portions of the job and counter bid in response to requests for bids. Control programs are simply developed and the potential exists for control programs to be quickly changed as new circumstances develop. Examples of this would be if it is desired to produce a new product or if ACUs (and associated equipment) are introduced or removed from the system. A description of some such of autonomous control systems are described in co-pending patents.
For an autonomous cooperative system to produce an optimized outcome, it is desirable that many different of divisions of the job among the ACUs be explored and thus that a large number of bids be collected from many different ACUs. This is done by allowing each ACU to make multiple simultaneous requests for bids from other ACUs. It follows that a single ACUs may receive multiple requests for bids from multiple other ACUs each of which must be considered in a separate “context” and each of which may mature into a different completed bid.
The bidding process for each context requires a large number of bidding messages be transmitted over the network 16. Such messages generally include “bid requests” and replies to bid requests including “bid success”, “bid failure” and “counter bid” messages. The numbers of messages increases geometrically with the number of ACUs involved and these messages can easily overtax even high-speed communication networks thus delaying the determination of a control solution. This delay limits the usefulness of an ACS in responding quickly to changing control situations and effectively limits the size of control problems that may be advantageously handled by the ACS.
What is needed is a way to realize a freely scalable ACS system that may rapidly determine an optimized control solution that may be implemented with existing hardware having network bandwidth and processing limitations.